Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. An example of a molded article that can be formed, for example, from polyethylene terephthalate (PET material) is a preform suitable for subsequent blow molding into a final shaped container.
A typical injection molding machine includes a material hopper, an injection unit (e.g. a screw-type plunger), and a heating unit. With injection molding, granular plastic is typically fed by gravity from a hopper into a heated barrel. As the granules are moved forward by a screw, the plastic is forced into a heated chamber, where it is melted. As the screw advances, the melted plastic is forced through a nozzle that rests against the mold, allowing it to enter the mold cavity through a gate and melt distribution system, e.g. hot runner system. Hot runner systems are used in molding systems, along with mold assemblies, for the manufacture of plastic articles. Usually, hot runner systems and mold assemblies are treated as tools that may be sold separately (or together) from molding systems.
A hot runner system is typically comprised of several components: a sprue to receive molten resin from the injection nozzle, a manifold to distribute the resin to several ports, and a plurality of nozzles to transfer the resin from the manifold ports to the receiving molding cavities in the mold. Each of these components may have a different material composition, due to desired thermal, strength, or wear characteristics. Different material types result in differing rates of thermal expansion for the components. This may be understood as relative motion between the components during the heat up and cool down phases of operation. High thermal conductivity is often desirable for hot runner components.